1. Field of the invention
This invention relates to a reductive method of bleaching de-inked paper pulp, and removing ink particles therefrom.
In recent years there has been a substantial increase in the recycling of newsprint, magazines and other paper which has a significant content of printing ink.
2. Description of the Prior Art
In conventional processes, pulp containing recycled paper is subjected to an oxidative de-inking process to release ink particles from the fibres. The resulting pulp is however likely to have a grey or yellowish color and must be subjected to a further bleaching step, for example using sodium hydrosulfite, and possibly also the addition of kaolin.
Kaolin and the chemicals used in bleaching such as sodium hydrosulfite and sodium borohydride are expensive, and bleaching may still not be entirely satisfactory if ink particles remain in the pulp.